The present invention relates to a spinal implant set including a quick closure device according to the preamble of claim 1.
Such closure devices are typically used in the surgical treatment of the spine. As the patients are increasingly aged, they have more often porotic bones, thereby limiting the anchoring ability of screws. It is therefore particularly important that connecting elements can be fastened in screw heads with minimum stress, ideally in such a manner that the screw anchorage in the bone remains unaffected.
Various quick closures are known in the art, all of which suffer from one or several drawbacks, however, as shown below.
For their comparative assessment, quick closures of the prior art are classified as follows: Internally or externally slidingly attachable quick closures, internally or externally rotatively attachable quick closures, as well as internal and external bayonet-like quick closures. Also, a vertically snapping quick closure is referenced in the prior art.
Among the internally slidingly attachable quick closures, the following ones are e.g. known in the art: EP0672388 (Metz-Stavenhagen et al., 1995), slidingly insertable with an end stop in the insertion direction; U.S. Pat. No. 6,110,172 (Jackson, 1998), insertable from two directions with an end stop in both directions after raising the cap; U.S. Pat. No. 6,302,888 (Mellinger, 1999), insertable without end stops. EP0836436 (Wisnewski et al., 1995), not only slidingly but pivotably insertable without end stops.
Among the externally slidingly attachable quick closures, the following ones are e.g. known in the art: DE4107480 (Ulrich et al., 1991) and U.S. Pat. No. 6,139,549 (Keller, 1997), insertable at the bottom of the screw head near the bone thread without stops and with high space requirement.
Among the internally rotatively attachable quick closures, the following ones are e.g. known in the art: EP1119304 (Yuan, 1998), rotatively insertable in one direction with an end stop; U.S. Pat. No. 6,258,090 (Jackson, 2000), rotatively insertable in one direction without an end stop; U.S. Pat. No. 6,652,526 (Arafiles, 2001), rotatively insertable in two directions without an end stop; U.S. Pat. No. 6,786,903 (Lin, 2002), rotatively insertable in two directions with a positioning aid on the rod.
Among the externally rotatively attachable quick closures, the following ones are e.g. known in the art: U.S. Pat. No. 5,346,493 (Stahurski et al., 1993), rotatively insertable in both directions without an end stop; U.S. Pat. No. 6,251,112 (Jackson, 2000), rotatively insertable in one direction without an end stop; EP1190678 (Bono et al., 2001), rotatively insertable in one direction with an end stop.
Among the internal and external bayonet-like quick closures, the following ones are e.g. known in the art: DE9403231 (Aesculap, 1994), insertable at the bottom of the screw head from one side, with an end stop; U.S. Pat. No. 7,235,075 (Metz-Stavenhagen, 2003), insertable at the top of the screw head from one side, with an end stop.
A snapping quick closure is proposed by US 2005/0027292 (Bernard et al., 2005).
In this respect, a main disadvantage of slidingly insertable quick closures is that relatively high moments have to be applied to the typically long instruments used in spinal surgery by the surgeon with the risk of creating uncontrolled situations at the location of the screw. For rotatively insertable quick closures, the required torque along the instrument always remains the same. A rotational insertability from two sides is therefore important as due to the increasingly frequent application of dynamic stabilizing systems, plastic rods are being used more and more frequently. They are, however, larger than metal rods for reasons of stability and therefore require more space.
In situations of limited space at the pedicle entrance, a quick closure that is rotatively insertable from only one side may lead to collisions with transverse processes or facet joints, which is less probable in the case of a rotational insertability from two sides. With quick closures without end stops, screws cannot be tightened without being retained by an additional instrument for which the access to the screw is difficult. Consequently, an end stop in the tightening direction preserves the bone bed while fastening the clamping screw whereas an end stop against the tightening direction preserves the bone bed while releasing the clamping screw. An end stop in both directions optimally preserves the bone bed in both directions.
A major disadvantage of a metallic snapping mechanism are the required macroscopic elastic deformation achievable only through limited local strength and the rather complicated instruments required to unlock a snapped-in junction while demanding important removal forces with the risk of overloading the elastic elements. Also the tightening screw of Bernard et al. does not have a matching seat in the screw head and consequently cannot transfer the rod's load directly into the screw head, but must rather transfer them through the threads of the closure.
Also as a result of the increasing dimensions of plastic rods for dynamic stabilizing systems, the space left between the screw head and the pedicle entrance is mostly insufficient for a quick closure coupling. In such cases, only systems are applicable where the quick closure is arranged at the top of the screw head.